1. Field of the Invention
The invention relates to wastewater treatment in general and to methods of controlling odors during treatment in particular.
2. Prior Art
Objectionable odors are caused by a variety of substances typically present in wastewater. These include sulfur and several sulfur containing compounds including hydro sulfuric acid, sulfuric acid, mercaptans (R—SH) including especially methyl and dimethyl mercaptans, and dimethyl disulfide (DMDS); numerous organic acids including propionic acid, acetic acid, butyric acid, isovaleric acid; ammonia; urea; and various terpenes including carene, pinene, limonene. These substances most frequently lead to noticeable odors under anaerobic conditions.
There are several approaches to odor problems known in the art. One solution is to add masking agents and perfumes to the wastewater. Obviously, such measures do not solve the problem, but only cover it up. Another solution is to add aerating equipment. These measures are frequently successful, but they can be very expensive, both from the standpoint of capital spent on the equipment itself and in terms of increased operating expense.
Chemical oxidizers, such as ozone; chlorine dioxide; and hydrogen, calcium, or magnesium peroxide, may be added to wastewater to alleviate anaerobic conditions. Although these methods can be effective, they are usually very expensive. This expense pressures managers of wastewater facilities to minimize the amount of oxidizers added to the system. The need to economize can be detrimental if it leads to underdosing. Underdosing can cause incomplete or partial oxidation, which can create worse odor problems than those the oxidants were introduced to cure. When chlorine dioxide is added to organic acids, incomplete oxidation can cause the formation of chloroacetic acid, which has a foul odor noticeable at very low concentrations.
Another method is to add neutralizing amines, which form stable salts with sulfide compounds. These may be effective against sulfide compounds, but do not treat other sources of odors such as organic acids. Additionally, amines suffer the same disadvantage as all chemical treatments. The chemicals are consumed in the reaction with the sulfur compounds in the wastewater, requiring new chemicals to be added if more sulfur compounds enter the wastewater treatment facility.
It is also known to add bacteria and enzymes to the wastewater to combat the odor causing substances. Again, these methods are frequently effective, but their results are often short lived. Typically, the evolution of odors from wastewater treatment lagoons will be due at least in part to the presence of undesirable bacteria in the lagoon. Unless the conditions that gave rise to the undesirable bacteria are rectified, the newly added bacteria will usually not be able to predominate, and the bacterial population will eventually return to its pre-treatment composition. As that occurs, the odors associated with the original population will return as well. Accordingly, an odor control method meeting the following objectives is desired.